The non-motile aeromonad, Aeromonas salmonicida that belongs to the family Aeromonadaceae, is the causative agent of bacterial septicemia and furunculosis in a broad variety of fish, and it has caused significant economic losses in worldwide aquaculture (Wiklund T, Dalsgaard I (1998) Occurrence and significance of atypical Aeromonas salmonicida in non-salmonid and salmonid fish species: a review. Dis Aquat Organ 32:49-69). Recently, the emergence of antibiotic-resistant Aeromonas salmonicida strains in aquaculture has been recognized as great concern including Korea (Kim J H, Hwang S Y, Son J S, Han J E, Jun J W, Shin S P, Choresca C H, Choi Y J, Park Y H, Park S C (2011) Molecular characterization of tetracycline- and quinolone-resistant Aeromonas salmonicida isolated in Korea. J Vet Sci 12:41-48). Particularly, although it was reported that in 1951, Aeromonas salmonicida, which is most frequently used in fish aquaculture, already acquired resistance to oxytetracycline, it is now used multilaterally. Moreover, the emergence of resistant bacteria caused by the abuse of antibiotics against Aeromonas salmonicida and also R-plasmids encoding antibiotic resistant bacteria were also reported. Further, generation of resistance to a second generation antibiotics of 4-quinolones-fluoroquinolones, notably enrofloxacin and sarofloxacin, was also reported. Therefore, alternative control methods are urgently needed.
Theoretically, phage can be used to treat pathogenic bacteria, as an alternative approach to control infectious bacterial disease. In practice, phage has been used as therapeutic or prophylactic agents against several fish and crustacean pathogens (Karunasagar I, Shivu M M, Girisha S K, Krohne G, Karunasagar I (2007) Biocontrol of pathogens in shrimp hatcheries using bacteriophages. Aquaculture 268:288-292; Kim J H, Gomez D K, Nakai T, Park S C (2010) Isolation and identification of bacteriophages infecting ayu Plecoglossus altivelis altivelis specific Flavobacterium psychrophilum. Vet Microbiol 140:109-115; Munro J, Oakey J, Bromage E, Owens L (2003) Experimental bacteriophage-mediated virulence in strains of Vibrio harveyi. Dis Aquat Org 54:187-194; Nakai T, Park S C (2002) Bacteriophage therapy of infectious diseases in aquaculture. Res Microbiol 153:13-18; Vinod M G, Shivu M M, Umesha K R, Rajeeva B C, Krohne G, Karunasagar I, Karunasagar I (2006) Isolation of Vibrio harveyi bacteriophage with a potential for biocontrol of luminous vibriosis in hatchery environments. Aquaculture 255:117-124). Likewise, experimental applications of phages related to control Aeromonas salmonicida have been reported using phage HER110 (Imbeault S, Parent S, Lagace M, Uhland C F, Blais J F (2006) Using bacteriophages to prevent furunculosis caused by Aeromonas salmonicida in farmed brook trout. J Aquat Anim Health 18:203-214) and phage O, R and B (Verner-Jeffreys D W, Algoet M, Pond M J, Virdee H K, Bagwell N J, Roberts E G (2007) Furunculosis in Atlantic salmon (Salmo salar L.) is not readily controllable by bacteriophage therapy. Aquaculture 270:475-484).
However, to date, a number of Aeromonadaceae infectious phages have been isolated and characterized, but according to the VIIIth ICTV report (http://www.ictvdb.org/Ictv/index.htm), most of them were classified into Myoviridae as P1, P2 and T4-like phages. Moreover, recent studies of Aeromonas phage have focused on virulent T4-like phage. Other Aeromonas phages that belong to Myoviridae but not classified as T4-like phage have not been investigated, with the exception of Aeromonas phage φO18P, which has been investigated and classified as P2-like phage and infects Aeromonas media, but its infectivity against Aeromonas salmonicida has not yet been reported.
The Vibrio parahaemolyticus is a gram-negative bacillus, which belongs to the family Vibrionaceae, and is known to infect a person, who has an underlying disease in a compromised immune state such as liver diseases, alcoholism and diabetes, eats fish and shellfish infected with raw bacteria or incompletely cooked food, or has a wound that is exposed in contaminated seawater. In many countries including Korea and Japan, its occurrence is continuously growing every year due to habits of eating raw fish and shellfish, and is known as a huge problem due to its high collective occurrence. Recently, according to the increase of eating raw fish and shellfish in many countries in the West, outbreaks of disease caused by the bacteria infection is spreading all over the US, Europe, and across the world. This infectious disease is known to be closely related to particularly oyster, and because these bacterias actively reproduce when water temperature rises, sale and distribution of oyster are banned every summer, particularly during June-September when they are the most prevalent. Particularly, extra precaution is demanded due to the increase of group meals and the like which could lead to a pandemic.
The motile Aeromonas, Aeromonas hydrophila belonging to the family Aeromonadaceae, infects a broad variety of fish and causes septicemia, bleeding, an ulcer and the like, and mass mortality, resulted therefrom, cause significant economic losses. Particularly, in domestic aquaculture farms, Aeromonas hydrophila disease can become strongly infectious due to breeding performed in very crowded and limited spaces. Most representative examples of such aquarium fish are, carp and goldfish, which are severely damaged by Aeromonas hydrophila in fish farming markets all over Jincheon, Chungcheongbuk-do.
The Aeromonas hydrophila, which is an underwater resident flora, is prevented by treating with antibiotics thereto in many cases. Consequently, most of the Aeromonas hydrophila show resistance against antibiotics, and the remaining antibiotics becomes a threat to national health and also damages caused by the occurrence of resistant bacteria becomes more severe.
On the other hand, bacteriophage is a virus that specifically infects bacteria, and was founded by Twort, an English bacteriologist, in 1915, during his research on the phenomenon that micrococcus colony when decomposed turns the bacterial transparent. Also in 1917, a French bacteriologist d'Herelle found out that there was something that decomposes Shigella disentriae in filtrate of feces of a patient with dysentery, and continued to study to identify the material, leading to the finding of bacteriophage which means “eating bacteria”. Therapeutics using phage, have been continuously studied only in East Europe and Soviet after the development of antibiotics. However, recently, because multidrug-resistant pathogenic bacteria and super bacteria resulted from over-use and/or mis-use of antibiotics have been frequently reported, and many problems of the conventional antibiotics have emerged, it has gained attention as an alternative for antibiotics. Moreover, bacteriophage has advantages in terms of short development time and low development costs, bacteria selectivity, sustainability, side effects and the like in comparison to antibiotics.